You have the option of watching the videos at various speeds (25% faster, 50% faster, etc). To change the playback speed, click the settings icon on the right side of the video status bar.
- Video Course
- Video Course Overview
- General GRE Info and Strategies - 7 videos (free)
- Quantitative Comparison - 7 videos (free)
- Arithmetic - 42 videos
- Powers and Roots - 43 videos
- Algebra and Equation Solving - 78 videos
- Word Problems - 54 videos
- Geometry - 48 videos
- Integer Properties - 34 videos
- Statistics - 28 videos
- Counting - 27 videos
- Probability - 25 videos
- Data Interpretation - 24 videos
- Analytical Writing - 9 videos (free)
- Sentence Equivalence - 39 videos (free)
- Text Completion - 51 videos
- Reading Comprehension - 16 videos
- Study Guide
- Philosophy
- Office Hours
- Extras
- Prices
Comment on Find the 3-Part Ratio
For the first question - how
a:b:c=2c:3c:6c
*divide both sides by c*
a/c:b/c:c/c=2:3:6
That isn't how EQUIVALENT
That isn't how EQUIVALENT ratios work.
If we take a ratio (not an equation) and multiply or divide it's PARTS by some non-zero value, we create an EQUIVALENT ratio.
So, for example, we can take the ratio 10 : 35, and divide both parts of the ratio by 5 to get the EQUIVALENT ratio 2 : 7
That is, 10 : 35 = 2 : 7
Likewise, we can take the ratio 2c : 3c : 6c and divide all the parts by c to get 2 : 3 : 6
That is 2c : 3c : 6c = 2 : 3 : 6
So, as the solution tells us...
a : b : c = c/3 : c/2 : c [via substitution]
= 2c + 3c + 6c [we took the previous ratio and multiplied all 3 parts by 6]
= 2 + 3 + 6 [we took the previous ratio and divided all 3 parts by c]
Does that help?
At 1:41 I'm confused as to
You're referring to 1:30 in
You're referring to 1:30 in the above video.
Here we must convert c/3 : c/2 : c into an equivalent ratio.
If we multiply each term by 6, we get: 6c/3 : 6c/2 : 6c
When we simplify each term by 6, we get: 2c : 3c : 6c
Now let's see what happens when we DIVIDE each term by 6.
We get: (c/3)/6 : (c/2)/6 : c/6
Rewrite 6 as 6/1 to get: (c/3)/(6/1) : (c/2)/(6/1) : c/(6/1)
Invert and multiply: (c/3)(1/6) : (c/2)(1/6) : c(1/6)
We get: c/18 : c/12 : c/6
While this new ratio is still EQUIVALENT to c/3 : c/2 : c, it doesn't match any of the answer choices.
For more information about eliminating fractional expressions, watch: https://www.greenlighttestprep.com/module/gre-algebra-and-equation-solvi...
Cheers,
Brent
For this question, does this
Since c / a = 3, then a / c = 1 / 3, meaning, a : c = 1 : 3
Similarly, since c / b = 2, then b / c = 1 / 2, meaning, b : c = 1 : 2
To link a : c to b : c, we will use c. The only way we can link c is to make c in both a multiple of both 3 and 2. Here, we will use 6. In the first ratio, we get a : c = 2 : 6 and in the second ratio, we get b : c = 3 : 6. To put it together, we get a : b : c = 2 : 3 : 6.
Did that approach make sense? Thanks fo your time.
Hey stomer,
Hey stomer,
That's a completely valid approach. Nice work!
Cheers,
Brent
Hi, why does the rule 'if a/b
Everything you stated is
Everything you stated is entirely true (1c = 3a and 1c = 2b), but what steps did you take to conclude that a:b:c = 1:2:3?
Once I see your solution, I'll be able to help more.
Cheers,
Brent
Sorry, I misspoke above. I
Be careful. If 1c = 3a, then
Be careful. If 1c = 3a, then a : c = 1 : 3
Here's why.
Take: 1c = 3a
Divide both sides by c to get: 1 = 3a/c
Divide both sides by 3 to get: 1/3 = a/c
In other words, a : c = 1 : 3
Likewise, if 1c = 2b, then b : c = 1 : 2
Cheers,
Brent
Hi Brent,
This is how I worked this problem.
If c/a=3, then c/a = 3/1 (c=3, a=1 )
If c/b=2 , then c/b = 2/1 (c=2, b=1 )
C is a common term in both ratios, so combine them by creating equivalent ratios.
Multiply first ratio by 2 and second one by 3
c/a = 6/2
c/b = 6/3
From the above, a = 2, c=6 and b = 3
So, a:b:c = 2:3:6.
Please let me know if this works :)
That approach is perfect.
That approach is perfect. Nice work!